THE STORY OF GÜNTHER and Reinhold's final climb together began with great promise in 1969, when the two Tyrolean brothers were thrilled to accept invitations to join a team tackling the first ascent of the Rupal Face on Nanga Parbat, a mountain known to be a killer.

Reinhold was a hotshot climber in the Alps, determined to make a career out of mountaineering. Günther—reticent, devoted, and deferential to his older brother—was a talent in his own right. He and Reinhold, part of a family of nine children, had grown up in the Villnöss Valley, in the Italian Dolomites, surrounded by formidable crags and walls that became their training ground—and their escape route from their authoritarian father. They'd bonded after an incident that occurred when Reinhold was 13.

"Reinhold says he's got his honor back," says Max von Kienlin, a veteran of the 1970 Nanga Parbat expedition who thinks Messner might have abandoned his brother on the mountain. "But why, if he left Günther?"

"I found my younger brother Günther cowering in a dog kennel," he writes in The Naked Mountain. "Our father, during one of his fits of rage, had thrashed Günther so badly with the dog whip that he could no longer walk." From that day forward, the two became climbing partners and allies, united against "the injustices of this world."

The other members of the expedition included some elite climbers: Saler, Gerhard Baur, Felix Kuen, Peter Scholz, and Jürgen Winkler, a photographer. The suave von Kienlin had offered a cash contribution in return for being included.

Their leader was the taciturn 54-year-old Karl Maria Herrligkoffer, who'd already organized six expeditions to Nanga Parbat. (He'd become obsessed with the mountain after his half brother, climber Willy Merkl, along with eight others, died on the peak in 1934.) He'd also commanded the 1953 trip in which maverick climber Hermann Buhl—defying Herrligkoffer's demands to return to base camp—made the first ascent of Nanga Parbat, a fast-and-light solo above the high camp on the Rakhiot Face. Herrligkoffer had not been pleased at Buhl's rebel impulse. Messner, for his part, idolized Buhl's breakaway spirit.

But on June 26, 1970, no defiance seemed evident. High on the mountain, the Messners and Baur sat at Camp 5, watching for a signal rocket from base camp. If Herrligkoffer fired a blue rocket, it meant good weather, and the team would try to summit on the 27th. If Herrligkoffer fired a red rocket, it meant bad weather, and Reinhold would attempt a Buhl-like solo dash.

Radio Peshawar reported good weather, so Herrligkoffer fired a rocket, but it exploded red, not blue—the first glitch. Seeing this, Messner started out shortly after 2 a.m., without gear, for a quick-and-light attack, to avoid the presumed bad weather. At sunrise, as Günther and Baur were installing rope to aid Reinhold's return, Günther did something impulsive—the second crucial twist in the tragedy.

Baur, now a 58-year-old adventure filmmaker based in Bavaria, recalls how Günther impatiently dumped a rope and sprinted into the Merkl Couloir, a nearly 2,000-foot ice ribbon, to catch up with his brother. It was the last time anyone but Reinhold saw him.

As Messner describes it, he was at first irritated but eventually glad when a breathless Günther—he had pulled off the amazing feat of climbing the steep face, at altitude, in less than four hours—appeared for the final push. The brothers reached the summit at about dusk, shook hands, then started down. Immediately, Günther began lagging, addled from his fast climb. Günther worried that reversing down the sheer Rupal Face would be dangerous. He suggested a descent via the gentler Diamir Face.

Slowly, Messner came around to the idea, he writes in The Naked Mountain. The Diamir Face looked like the only way out of desperate straits—the brothers had no stove, tents, food, or sleeping bags. ("You think I was so crazy that I would plan to traverse Nanga Parbat without a cooker?" as Messner would ask me later. "I'm not stupid!")

In Messner's account, they descended for about 800 feet to the Merkl Gap, a notch in the southwest ridge named in honor of Herrligkoffer's half brother. From there, Messner could peer down into the Merkl Couloir—the route they'd used that morning. The brothers bivouacked in the gap, in temperatures as low as 40 below zero.

The next morning, Messner recalls, Günther was delirious. The older brother says he started shouting for help at 6 a.m. About three hours later, he saw Kuen and Scholz in the Merkl Couloir, heading for the summit. Messner says he shouted to Kuen for help and a rope, but it was windy, he was yelling over a cliff, and Kuen was as far as 100 yards away. Kuen and Scholz climbed higher, then Kuen and Messner tried again. Günther was out of sight; Kuen did not know where he was.

"Are you both OK?" Kuen yelled.

"Yes! Everything's OK," Messner replied, in what would become one of the central puzzles in the dispute. Why, Messner's teammates would challenge later, did he not signal their distress?

It's impossible to get elaboration from Kuen or Scholz, because both have died, Kuen in 1974 and Scholz in 1972. But according to Messner, the brothers were OK, relatively speaking: They were alive, just badly in need of a rope.

Messner says he then tried to coax Kuen and Scholz to climb up to him, but Kuen judged the steep, corniced wall between them to be suicidal. So, thinking the brothers were indeed OK, Kuen and Scholz continued toward the summit, leaving Messner, by his own account, in utter despair.